A compass, is a drawing tool. It can be used for drawing circles or arcs.
It can also measure distances on a drawing or maps. Compasses are used in geometry, and design.
Compasses are usually made of metal, plastic or a combination of both. A simple compass has a hinge.
The hinge, which can be tightened with a screw driver, can be adjusted. This allows the arm to move changing the radius.
One part has a solid sharp point at its end, and the other end has a pencil, scriber, pen or marker.
I purchased the beam compass at Loeb’s for about fifteen dollars.
Beam compasses allow you to draw much larger circles and arcs.
Use the correct screwdriver to tighten the adjustable arm, if necessary.